A large group of receptors which mediate the actions of a number of hormones and neurotransmitters are coupled to the activation or inhibition of intracellular enzymes by GTP-binding regulatory proteins (G-proteins). The activated G-proteins serve as transmitters of information to the interior of cells. We have, for many years, Concentrated our efforts on two of the G-protein-coupled receptors: those for the opiates and for bradykinin. The neuroblastoma x glioma hybrid cell line, NG108-15, is richly endowed with both of these receptors, and is particularly attractive since it expresses only one of the many opiate receptors found in brain. In the past year we have focused on the isolation of peptide fragments of opiate receptors and the determination of their amino acid sequences. A collaboration has been arranged for determining the amino acid sequences of the fragments after their separation by micro-bore HPLC columns. We expect to use this sequence information to isolate cDNA clones coding for the opiate receptor in order to learn its complete amino acid sequence and to be able to study the regulation of its synthesis. By the combined use of specific antibodies and synthetic peptides we characterized a receptor domain that activates G-proteins, and showed that no other intracellular domain fully shares these properties. We expect to extend these studies by preparing synthetically fused intracellular domains of receptors. Our many attempts to prepare crystals of one of several brain G protein have so far failed, as have those of a number of other laboratories similarly engaged. Although it is always difficult to draw conclusions from negative results, it seems possible that the G-proteins may not take up a single predominant conformation in solution because they are designed to easily cycle between several different structures in the exercise of their modulatory functions. Our solubility studies suggest that there are large differences in conformation depending on the state of the proteins and more detailed conformational studies are clearly called for. In related work, we are carrying out studies aimed at improving the methods for predicting the three dimensional structures of proteins based upon amino acid sequence information.